contrib: install PyOxidizer 0.16.0 PyOxidizer now provides MSI installers and pre-built Linux binaries. So we install that way. This significantly reduces the time to bootstrap a new machine in automation, as building PyOxidizer from source on a low core count machine takes several minutes. This change temporarily breaks the ability of the automated environment to use the in-repo pyoxidizer.bzl configuration file, as there are backwards-incompatible changes with the upgrade that need to be reflected. We'll handle those in subsequent commits. Differential Revision: https://phab.mercurial-scm.org/D10680